The accounts list may get very high if the number of accounts is important (here ~30, screen 1080px high, it nearly outbound). The mainwindow follows this tabs list, is not resize-able and potentially goes off screen.
Implemented in: http://git.claws-mail.org/?p=clawsker.git;a=commitdiff;h=c72062640563296693da72a3645239c9f5a25c36